Migrant children are a special group in the process of China’s economic development. They not only linger on the edge of unequal educational opportunities, but are also marginalized in schools. Using data from the China Education Panel Survey (CEPS), a nationally representative sample of junior high school students, the study attempts to examine the relationship between migrant children’s marginalization and academic achievement, and check the moderating role of teacher support in this relationship. The results show that positive teacher support has a negative moderating effect on the marginalization of migrant children. When teachers take a positive and supportive attitude toward socially marginalized students, the marginalized children are more integrated within their peer groups over time. The more actively teachers support migrant children, the more they can reduce the probability of migrant children being marginalized. Teacher support also has a positive impact on migrant children’s social  behavioral development and  academic performance to a large extent. The positive attitude of teachers enables migrant children, a marginalized group, to have stronger school adaptability and a more positive development direction of social behavior and academic performance.